1. Field of the Invention
The invention relates to processes of initializing disks for optical data storage.
2. Description of the Related Art
In a phase transformation optical recording medium, data is generally recorded by transforming the phase of each recording bit of the recording layer from a crystalline state to an amorphous state. In general, since recording is conducted using phase transition between the two states, the phase of the recording thin film should be converted to the crystal phase in advance. This operation is called initialization, signifying the transformation of the whole recording region on the recording layer to the crystalline state prior to the recording of data. One method of initialization, typically referred to as serial processing, uses a laser beam for initialization. With this method, a laser light spot of from several tens to several hundreds of xcexcm in diameter is formed with the output far greater than that of a typical laser diode for recording and reproduction. By irradiating and rotating the media at a constant speed, many tracks can be crystallized in a single operation. This method has the advantage that the medium is heated in a small area at a time, reducing thermal load and the consequent risk of material cracking. However, because only a small area is illuminated at any one time, this method has the disadvantage that initialization of an entire disk takes a long time. To overcome some of the difficulties associated with serial methods of optical initialization, flash methods of initialization have been developed. By irradiating the media with a flash lamp, the recording layer across the entire surface of the optical recording medium can be initialized simultaneously. With initialization by flash irradiation, the initialization itself may be completed in a period of only several milliseconds. One problem with this method, however, is that the recording medium is heated at once, producing thermal induced internal stresses that increase the likelihood of thermal damage to both the substrate and the coating, such as warping, cracking, and other forms of distortion. In U.S. Pat. No. 5,684,778 to Yamada et al., this problem is addressed by controlling the duration of the flash. As the flash duration decreases, however, flash intensity must be increased to successfully produce the desired phase change in the recording material. This requires a resulting increase in power supply capacity and expense, and also increases the time required to charge the flash capacitor, thereby slowing any process of sequential initialization of disks during the disk manufacturing process. Other attempted solutions include the use of a complex thermal heat management platten. Another problem with the flash initialization method is that the uniformity of initialization over the disk surface is difficult to produce. Spatial non-uniformity in the light intensity of the flash produces non-uniform initialization. In addition, the structure of the disk results in a reflectivity profile which varies significantly depending on wavelength and angle of incidence. A single flash, therefore, will typically produce a non-uniform initialization that has heretofore been unacceptable for the production of optical disks intended for high density data storage. Making the illumination more uniform with, for example, an optical tunnel is very inefficient and requires higher input flash power with the associated problems outlined above.
The present invention relates to a method of initializing an optical recording media. In preferred embodiments, this process will comprise the exposure of the media to at least two flashes of light. These flashes are preferably less than about five hundred micro-seconds in duration, and are preferably repeated at a rate of at least one flash per second. In other embodiments, the flashes may be repeated five or more times, and for 100 to 200 microseconds per flash. These repetitions may occur as frequently as 10 to 50 flashes per second. For example, five 150 microsecond flashes repeated at a rate of 30 Hz.
In accordance with another aspect of this invention, an apparatus is provided for initializing optical recording media. This apparatus preferably comprises one or more flashbulbs, a support for the media to allow adjustable proximaty to the flashbulbs which may be rotatable (for off-line initialization) or a support for the flash head that allows adjustable proximity to the media for in-line initialization, a capacitor, a charging circuit, a switching circuit coupling the capacitor to the charging circuit. Additionally, the control circuit is preferably configured to repetitively charge the capacitor with the charging circuit and to discharge the capacitor through one or more of the flashbulbs at a rate of at least about one discharging and charging cycle per second. In preferred embodiments, the flashbulbs may be a spiral shape. Preferably, the spiral begins with a connector proximate to the center of the spiral, and ends with a connector proximate to the center of the spiral as well.
In accordance with another aspect of this invention, a method is provided for initializing optical recording media comprising exposing a layer of material of the media to a series of two or more low energy, high duty-cycle flashes of light. In further embodiments, this method may comprise a series of two or more low energy, high duty-cycle flashes of light wherein each of the flashes has sufficient intensity and duration to only partially crystallize the layer of material.
In another preferred embodiment of this invention, an apparatus for initializing an optical recording medium is provided comprising a flashbulb having a substantially spiral shape, wherein the spiral begins and terminates proximate to the geometric center of the spiral, or terminates at the outside diameter, and wherein the spiral has an overall diameter which is approximately equal to or larger than the diameter of said recording media. A support for the media aligned with the flashbulb.
In yet another preferred embodiment of this invention provides for an optical recording media made a process comprising the steps of positioning the media proximate to a flashbulb and exposing the media to a series of two or more flashes from the flashbulb, wherein each flash successively increases a crystallization state of a layer of material on the media, or the fraction of the crystallized area on the disc, and wherein the layer of material is substantially completely crystallized by the series of flashes within approximately five seconds.